<p><br></p><section class="_135editor" data-role="paragraph" style="max-inline-size: 100%; margin: 0px; padding: 0px; border: 0px none; z-index: 0; overflow-wrap: break-word !important; outline: none 0px !important;"><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　在水平管道中,由于空气阻力的方向与流向相向而且与重力垂直,因此必须产生适当的力,使纤维介质悬浮,或至少使纤维介质间断上升,才能顺利地完成输送。在水平管道中,使纤维介质悬浮的力有两种,一种是因为一般气力输运中雷诺数较大而处于紊流状态,紊流具有垂直方向的分力。另一种是由于纤维介质的形状不规则,气流作用使纤维介质产生转动或沉于管道底部时,上面流速较大、静压较小,上下静压差产生升力。</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　在输送过程中,当纤维介质悬浮时,重力有使纤维介质下沉于管底的趋向,即产生纤维材料在管道中分布不匀。当纤维材料下沉至管底时,就与管底发生摩擦,速度降低,沿管壁滑动甚至翻滚,然后再跃起,形成螺旋式的运动。这种运动促使临界雷诺数降低,增加能量消耗并产生分层现象。如果流速再降低,就会在管道底部产生纤维沉积层,沉积层逐渐变厚后出现类似的腾涌与阻塞。</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　使棉块沿水平管道开始滑动时的气流速度称为启动速度;在纤维下降过程中,达到空气阻力与重力相等时的速度叫做终末速度;使棉块在水平管道中输送时保持悬空的气流速度,称为腾空速度。一般启动速度接近于终末速度,腾空速度可以根据理论公式推算,输送纤维或棉块时,可以按台维斯公式计算理论的腾空速度,亦可以按经验公式计算:</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　腾空速度vs =(2.4～3.7)vt</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　式中:vs ———腾空速度,m/s;</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　vt ———终末速度,m/s。</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　因此,在水平管道输送时,气流速度应较垂直管道中的大。</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　　在水平管道输送中,纤维介质的运动速度与流体的相对速度对管道输送有一定的影响,一般理论分析时,认为纤维介质运动速度应接近于气流速度。实际上由于所输送的棉块很多且大小不一,而且气流各点流速也不一致,再加上重力的影响,四面产生了棉块相互碰撞凝集及与管壁摩擦,使纤维介质的运动速度降低。根据理论推导与实践总结,几种物料的输送速度与混合比见下表。</p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;">　</p></section><section class="_135editor" data-role="paragraph" style="font-size: medium; 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